This invention relates to a preliminary mixing type gas burner, which enables a low noise, high load combustion, and more particularly to a gas burner which is used as domestic gas fixture.
There has been a demand for a domestic use of a high load combustion burner which produces low noise and is compact in size to fulfill a space requirement. However, there has been proposed no low noise, high load combustion gas burner in the past.
In a conventional type high load combustion gas burner, combustion of a turbulent nature takes place, resulting in high combustion noise. On the contrary, a burner of a low noise type tends to result in low load combustion.
A description will be made for conventional type gas burners of a low noise combustion type and a high load combustion type with reference to FIGS. 1 and 2.
FIG. 1 shows a gas burner, in which low-noise combustion takes place. Shown at 1 is a mixture gas passage for a mixture gas of gaseous fuel and primary air, with one end of the passage 1 being communicated with a mixture gas inlet 2, and the other end thereof forming a flame hole 3.
In operation, a mixture of primary air and gaseous fuel is supplied through the mixture inlet 2, then through the mixture passage 1 and out of a flame hole 3, thereby providing an inner flame 4 of a laminar flow and an outer flame 5 containing a large amount of H.sub.2 and CO in its trailing stream. A secondary air 6 flows along the outer periphery of the flame hole 3 at a flow velocity as low as 0.2 to 0.3 m/s and then is diffused and mixed with the outer flame 5. In this case, the inner flame 4 is provided in the form of a laminar flow, thus producing less combustion noise. Gas and primary air are mixed beforehand, so that the velocity of reaction takes place quickly, in which fuel in the inner flame 4 is decomposed into CO, H.sub.2 and the like, and hence a size of the inner flame 4 may be reduced. However, the outer flame 5 containing a large amount of CO and H.sub.2 is mixed with secondary air according to molecular diffusion, so that the size of the outer flame 5 is governed by a molecular diffusion velocity. However, a diffusion velocity is relatively low, taking a time as long as 100 to 200 ms, before the outer flame 5 is mixed with the secondary air completely, so that the size of an outer flame should be increased. As a result, a burner of this type provides a relatively low noise level, but suffers from a relatively small combustion-chamber load of an order of 10.sup.6 kcal/(h.m.sup.3).
FIG. 2 shows a gas burner of a high load combustion type. Shown at 1 is a mixture passage, with one end thereof being communicated with a mixture gas inlet 2, and the other end thereof having a plurality of mixture gas swirl vanes or blades 7. A secondary air passage 8 surrounds an outer periphery of the mixture gas passage 1, with one end of the passage 8 being communicated with a secondary air inlet 9, and the other end thereof being provided with secondary air swirl vanes or blades 10 in the neighborhood of an outer periphery of the mixture gas swirl blades 7.
In operation, primary air and gaseous fuel are supplied through the mixture gas inlet 2, then through the mixture gas passage 1 and out of the mixture gas swirl blades 7 in the form of a swirl. Secondary air is supplied through a secondary air inlet 9 and flows out of secondary air swirl blades 10 in the form of a swirl, followed by quick and vigorous mixing of secondary air and mixture gas. According to the burner of this type, a mixture gas is vigorously mixed with the secondary air, with the resulting quick decomposition of fuel into H.sub.2, CO and the like, as well as quick oxidation of CO and H.sub.2 into CO.sub.2 and H.sub.2 O, thus allowing a high load combustion on the order of 10.sup.7 kcal (h.multidot.m.sup.3). However, turbulence takes place, when fuel is decomposed into CO, H.sub.2 and the like, so that high combustion noise is produced. This has been clarified theoretically.